The present invention relates generally to scroll-type machinery. More particularly, the present invention relates to a scroll-type machine incorporating a drive bushing which is impregnated with a lubricant designed to be released under predetermined conditions.
A class of machines exists in the art generally known as "scroll" apparatus for the displacement of various types of fluids. Such apparatus may be configured as an expander, a displacement engine, a pump, a compressor, etc., and the features of the present invention are applicable to any one of these machines. For purposes of illustration, however, the present invention is disclosed incorporated into a hermetic refrigerant compressor.
Generally speaking, a scroll apparatus comprises two similar scroll members each of which includes a spiral scroll wrap upstanding from an end plate. The two scroll members are interfitted together with one of the scroll wraps being rotationally displaced approximately 180 degrees from the other. The scroll apparatus operates by orbiting one scroll member (the "orbiting scroll") with respect to the other scroll member (the "fixed scroll" or "non-orbiting scroll") to make moving line contacts between the flanks of the respective wraps, defining moving isolated crescent-shaped pockets of fluid. The spirals are commonly formed as involutes of a circle, and ideally there is no relative rotation between the scroll members during operation, i.e., the motion is purely curvilinear translation or orbital. The fluid pockets carry the fluid to be handled from a first zone in the scroll apparatus wherein a fluid inlet is provided, to a second zone in the scroll apparatus where a fluid outlet is provided. The volume of a sealed pocket changes as it moves from the first zone to the second zone. At any one instant in time, there will be at least one pair of sealed pockets, and when there are several pairs of sealed pockets at one time, each pair will have different volumes. In a compressor, the second zone is at a higher pressure than the first zone and is physically located centrally in the scroll apparatus, the first zone being located at the outer periphery of the scroll apparatus.
The concept of a scroll-type apparatus has thus been known for some time and has been recognized as having distinct advantages. For example, scroll machines have high isentropic and volumetric efficiency, and hence are relatively small and lightweight for a given capacity. They are quieter and more vibration free than many compressors because they do not use large reciprocating components (e.g. pistons, connecting rods, etc.) and because all of the fluid flow is in one direction with simultaneous compression in plural opposed pockets, there are less pressure-created vibrations. Such machines also tend to have high reliability and durability because of the relatively few moving parts utilized, the relative low velocity of movement between the scroll, and an inherent forgiveness to fluid contamination.
In one popular orbiting scroll compressor, a drive shaft is provided being rotatably supported by upper and lower bearings and has an eccentric pin drivingly coupled to the orbiting scroll member via a drive bushing. The drive bushing is rotatably disposed within a hub provided on the orbiting scroll and includes a slightly oval bore having a flat therein which allows for a generally radially directed sliding engagement between it and a corresponding flat on the eccentric drive shaft pin. This sliding engagement provides a radial compliance to the scroll compressor.
In order to lubricate the upper and lower bearings as well as the inside and outside surfaces of the bushing an oil sump is provided in the lower portion of a shell in which the compressor is disposed. The lower end of the drive shaft extends into this sump and includes an oil pump and a radially offset axially extending passage through which oil is supplied to the bearings and bushing.
Under certain flooded start circumstances, it has been discovered that a major portion of the lubricant from the sump may be discharged from the compressor to the air conditioning system of which the compressor forms a part along with the refrigerant. Because in such so-called split systems the compressor and condenser are typically located outside the building and the evaporator is located at some distance therefrom inside the building, a substantial time period may elapse before the discharged lubricant or oil is returned to the compressor. This time period may be as much as 6-10 minutes or even longer during which time the oil pump is unable to supply lubricant to the bearings and bushing. As a result the bearings and bushing will be running dry. This dry running will result in heating as well as wear of the bearings and bushing. The drive bushing is believed to be the most sensitive to such lubrication deficiencies perhaps because it is less able to dissipate heat to its surrounding structure (i.e. its position in the hub of the orbiting scroll which is also subject to heating by the compression process) and it will be the last bearing surface to receive lubricant once the supply has been replenished.
Compounding the problem is that in highly charged split heat pump systems which are installed during periods when substantial fluctuations in temperature are encountered and the system is not operated for an extended period of time, it is believed a strong reflux action occurs. This reflux action results in migration and cyclical condensation and vaporization of refrigerant in the compressor shell during these temperature swings. This cyclical condensation and vaporization of the refrigerant results in a washing action on the bearings tending to wash away any residual lubricant.
The present invention seeks to overcome this problem by providing a drive bushing which is impregnated with a suitable lubricant designed to be released therefrom during such periods of dry running. The ability to supply even a minimal amount of lubricant to the bearing surfaces of the drive bushing during the above described periods of insufficient lubricant supply will greatly reduce the potential for damage and/or premature failure of the sensitive drive bushing and hence prolong the operating life of the compressor.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.